Centrifuge for the dewaxing of oils



NGV. 4, 1941. H, Q LINDGREN I 2,261,394.

CENTRIFUGE FOR THE DEWAXIING 0F' OILS Filed May 24, 1938 a mi, 'l/ 23 2, 28

Patented Nov. 4, 1941 v CENTRIFUGE FOR THE DEWAXING OILS Appelviken, Sweden, as-

Hans 4010i Lindgren,

signor to Aktiebolage holm, Sweden,

t Separator-Nobel, Stocka corporationof Sweden Application May 24, 1938, Serial No.

In Sweden May 29, 1937 5 Claims. In centrifugal dewaxing of mineral oils, hydrogenated oils, etc., by the aid of Ia solvent added in order to make the oil suilclently fluid at low temperature, the precipitated wax moves either inward or outwardfin the centrifugal bowl depending on whether the oil solution is `heavier or lighter than the precipitated wax. In dewaxing with heavy solvents, the heavy solvents most commonly used are tri-Chlor ethylene, dichlor ethane and carbon tetrachloride, with or without addition of other liquids such as acetone, methyl ethyl ketone, methyl acetate or methyl formiate.

In the case of dewaxing with light solvents, naphtha or benzene are generally used, with or without similar additions. discharged from the centrifuge bowl as a more or less viscous mass. l t

It is very lmportant'that as small an amunt of oil as possible be discharged with the wak, as the escape of any oil with the wax involves substantial loss, owing to the great dilerencebetween, the prices of a high quality oil and wax. Consequently the centrifugal bowls are adjusted to produce as hard and dry awax as possible. Consequently the pressure required for discharging the wax becomes very high. In ordinarycentrifugal bowls this pressure can be generated only by displacing the boundary surface between Wax and oil from its natural position with regard to the specific gravities of the various media, the rate of throughput, etc. By so doing, however, the separating chamber of the bowl is not utilized in the best way; that is, the amount of oil which can be treated per time unit in the bowl becomes inferior to what it would be if the said boundary surface were correctly located.

It has therefore been suggested to discharge the wax by means of a skimming or paring device. -By changing the position of the orifice of this device in radial direction in relation to the rotation axis of the centrifugal bowl it is possible -to obtain wax of varying consistency. Experience has shown, however, that arrangements of this type can be used only if the wax mass be comparative'- ly uid. Otherwise the resistance to movement and deformation in the tube or channel system of the skimming device become too great.

My invention comprises a centrifuge which, while adapted for the separation from any liquid of solid matter lighter than the liquid, is more particularly intended and adapted for the separation of wax from a heavier oil solution, and

comprises means for insuring a more complete separation within the bowl of the wax and the In both cases the Wax is- ,in the art). channel-system 23 in which the various channels charge of the thus separated wax from the bowl l and also for imparting sufficient fluidity to the to enable it to be discharged device, and meansI whereby wax outowing wax through a paring may be allowed to escape from a. discharge channel communicating with the separating chamber of the bowl without flowing through the parer.

In the drawing: Fig. 1 is a vertical cross-section through a tion. Fig. 2 is a-horizontal section on the line 2 2 of Fig. 1. Fig. 3 is a view, similar to Fig. 2, of a modification. Y.

The liquid to be separated is introduced through the hollow spindle 2|, which advantageously communicates with the supply pipe for liquid by a packing device (not shown, but known In the bottom 22 of the bowl is a communicate as uniformly as possible with the centra1 hole in the spindle 2|. The channels of the system 23 also communicate positioned in the Wings 26 of the distributor 25. The open sidesy of the grooves are turned outward and they are provided with bottoms sloping inward and upward. The object of this arrangement is to obtain a uniform distribution of liquid in the pile of discs Z1, and to enable the solid particles which are separated already in the distributor to slide along the sloping bottom of the grooves upward and into the collecting chamber 28 situated inside the separating chamber as close to the overow 29 for using channels of this shape uniform distribution of the mixture, but also avoid vre-mixing of separated solids and liquid, which would occur if the mixture were supplied through vertical openings directly communicating with the system of channels 23. The lateral walls of the grooves are suitably used for guidingv the discs in known manner. It is important that'the channel system 23 should be located below the upper edge ofthe lowermost disc, as shown on the drawing. The separated solid particles thereby move similarly in radial direction, which results in the accumulation in the central part of the bowl of a symmetrical cylinder of separated solids. v q

From an examination of the distributing wings 26, it will belseen that the separated solids are compressed on their way towards the centre. As it may thereby occur in some cases that the solid matters become so hard that all movement I not only obtain a in direction inwards ceases, even if the pressure heavier oil solution, means facilitating the dis- 55l from the outside is increased to several kilograms per square centimetre, it may be advantageous to centrifuge'embodying my inven- Y with grooves 2d the solids as possible. By

construct the central portion according to Fig. 3A in which case there is no compression at all. In this flgure, 26 are the wings and 24' the discharge grooves therein.

In spite oi the precautionary measures indicated above, there is a risk that the time necessary for the solids separated at the bottom to travel to the overflow 29 at the top o! the bowl is so long that the solids are thereby very much dried. The result of this is that the movement in axial direction is rendered more diflicult. It has proved that ir the drying is driven too far, a layer may be-obtained which does not move at all. In order to avoid this, mechanical devices may be provided in the machine.

Fig. 1 shows a device of this kind, consisting or a member 40 which can be moved up and down. To the said member, elements 4I are fixed which work the inner side of the rotating layer of solids which is thereby prevented from becoming too heavy. I have found that it is generally possible with this simple device to keep such a plasticity of the solids in the inner part of the bowl that they can without difficulty be continuously discharged from the bowl.

Instead of an axially movable member it may in some cases be advantageous to have a fixed knife extending from way down into the central chamber 28, by which knife the solid matters are continuously peeled off. It may also be necessary to adjust the elements 4I during operation to different working depths in the solid layer,-and it may therefore be suitable to make them adjustable from the out- 4 side, for instance, by supports in the form or toothed rods. This connection with both fixed and axially movable elements. It is however possible that in the treatment of some liquids, solid matters are obtained for the transport of which more complicated arrangements are required. Arrangements for this purpose may be built according to a great many diierent principles. The member moving upwards and downwards may for instance be constructed as a paring device of about the same type as those used in cream separators. Such paring devices may be either disc-shaped or tubeshaped.

By making the device movable along the centre line of the bowl, the solid matters may be removed thereirom without having to move in the bowl in axial direction. It is further possible to arrange the paring device in container' provided inside Athe said device, the peeled-off mass being collected in the container and then being discharged from the bowl in any suitable manner. It is possible to buil-d a pump in the container, or to lift the container out of the bowl by mechanical means to empty and then to replace it. It is also possible to give the aforementioned element-s such a shape that the chips formed in chamber 28.

In the gure a bored channel 42 is shown in the central member 40, through which channel washing liquid can be introduced for Vwashing out as far as possible the liquid sticking to the solids. When a heavy diluent, for instance trichlor ethylene, is used in connection with separation oi an oil, containing wax, a bowl of the present type may be employed. It is then desirable that the wax should be as completely liberated from oil as possible, and this may be obtained by sprinkling on the surface of the wax oil-free trichlor ethylene, which is passed through the wax layer and thereby dissolves and removes part of the oil;w

the upper part the whole co-operation with a- In the further description of the separator lt will be assumed that the bowl is used in connection with the separation of wax. The separated wax enters the chamber 30 in which a discharge device Il is arranged. The liquid liberated from wax is conducted through channels I2 to an upper chamberl 23 in which a second` discharge device 34 is arranged.

A serious inconvenience with previously used centrifuges for this purpose is the high power consumption which is due to heavy gases, for instance of trichlor ethylene, penetrating to the chamber surrounding the bowl. In the present centrifuge, such gases are prevented from leaving the bowl by a packing device, consisting ci a chamber 35 iilled with liquid and into which a stationary disc 36 projects. This arrangement has substantial advantages as compared with those previously used, in which both wax and oil are thrown out into collecting vessels of the same typevas those used for open cream separators. Sealing liquid is fed to the chamber 35 through a pipe v43.

arrangement may be used in the peeling are thrown out or the participates inthe rotation ci In the case of dry wax it may be diilicult to discharge it through the paring device 2| illustrated, and step should therefore be taken to soften the wax. This may be eiected by introducing a diluting liquid the separated wax before it reaches the chamber, which liquid should be of the same kind as the one used as additional liquid during the separation. The additional liquid may advantageously be supplied through the member 40. In order to get effective mixing it has proved advantageous to have a relatively small play 31 between the bottom of the chamber 20 and the lower side of the paring device 4|. It may thereby in some cases be suitable to provide an axially movable disc in the bottom of the chamber, which disc the bowl and which is pressed on vthe stationary paring device by a suitable arrangement. With an arrangement of this type a very intimate mixing may be obtained. In order to prevent wax from overflowing from chamber 30 to chamber 33, or oil in the reverse direction in the case of unsuitable adjustment, it may be advantageous to provide an annular channel 38 between the two chambers which communicates with the atmosphere by openings 39. As it is desirable to work in ordi- 39 with automatic valves let through the lliquid leakvide these openings which intermittently ing out this way.

In a centrifuge of this type it is suitable to use regulating devices, which in principle are of the same type as those used in cream separators, for regulating the bowl so that wax and oil are discharged in the correct proportions; that is, as little oil as ispracticable should be contained in the wax when it is removed from the drying space of the bowl. Ii the plugs 44 are taken out, the wax can be removed directly from the bowl, without having to use the paring device 3 I. This may be advantageous if the wax becomes very hard.

'What I claim and desire to protect by Letters Patent is:

1. A centrifuge adapted for the separation of precipitated wax from an oil solution of higher speciiic gravity comprising a rotary bowl enclosing an annular outer zone extending to the periphery of the bowl, in which said separation is effected, and an inner central zone, surrounding the axis of the bowl, into which the separated wax is discharged and in which it accumulates, the bowl having at the upper end portion of said into the chamber 30 or to inner central zone an outlet through-which the 'severed wax is discharged, an axially positioned member extending into the central zone having a channel opening into the central zone below said outlet and through which diluent is adapted low said outlet and adapted to mechanically sever wax from the mass of wax accumulated in and moving toward said outlet.

2. A centrifuge adaptedfor the separation of precipitated wax from an oil solution of higher specific gravity comprising a rotary bowl enclosing an annular outer zone extending to the periphery of the bowl, in which said separation is eiected, and an inner central zone, surrounding the axis of lthe bowl, into which the separated wax is discharged and in which it accumulates, a distributor comprising an axial channel through which the mixture of wax and oil solution is fed and transverse branch channels from said axial channel leading 'outward to the inner lower part of the separating zone, and wings directly above the said transverse branch channels having upwardly extending grooves the lower ends of which are directly above and communicate with the discharge ends of said transverse channels, said grooves opening outward to the separating zone and having inner walls which extend ,upward and inward at a sharp angle to the bowls axis 3 rotating 'parer chamber, and means for closing and opening communication between said paring chamber and channel, the opening of said communication allowing wax to escape through said A rotating Vchan'nel without owing through the parer. g

4. A centrifuge in accordance with claim 2 in which the side walls of each groove extend at an angle to radii of the bowl.

5. A centrifuge adapted for the separation of precipitated wax from an oil solution of higher specific gravity comprising a rotary bowl enclosing an annular outer zone extending to the periphery of the bowl, in which said separation is effected, and an inner central zone, surrounding the axis of the bowl, into which the separated wax is discharged and in which it accumulates, the bowl having at the upper endportion of said inner central zone an outlet through which the separated wax is discharged, conveyor wings rotating with the bowl and extending into said inner central zone below said outlet, an axially positioned member extending into the central zone having a channel -through which diluent heavier than the wax is adapted to be fed and which has a discharge which opens outward into the central wax zone near said outlet and inside the inner edges of said wings, and mechanical means extending into said central zone and located below and spaced from said outlet and ex- .tending radially beyond the diluent discharge and the upper ends of which extend into said zonev of wax accumulation; enabling the wax separated in the 'distributor to slide along said Walls into the zone of w'ax accumulation.

3. A centrifuge for the separation of precipitated wax from oil which comprises a rotary bowl having a separating chamber and a paring charnber rotating with .the bowl and into which separated wax is adapted to flow, a stationary parer in the parer chamber for removing the wax iiowing thereintoMthe bowl having a discharge channel rotating with and adjacent one wall of the opening but inside the inner edges of the wings and adapted to work the inner side of the rotating mass of wax accumulated in said central zone while it is moving toward said outlet, the diluent fed through said discharge to the wax zone being adapted to pass through the separated wax layer and dilute and dissolve oil therein and also soften the wax and thereby cooperate with said mechanical wax-working means to insure the free movement of the wax toward said outlet.

HANS oLoF HNDGREN. 

